Corrosion-resisting metal



no 2 1 o 1 61 707 927 c. E. JONES ET AL.

CORROSION RESISTING METAL Filed Nov. 10, 1924 COATED WITH MOM/UM ,4/v0 7'//V V Inventors:

Charles E. Jones,

mark A.Atuesta,

The h" Attorney.

Patented Jan. 25, 19 27. I

UNITED STATES,

PATENT OFFICE.

CHARLES E. JONES AND MARK A. ATUESTA, OF SCHENEGTADY, YORK, AS- SIGNORS TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

CORROSION-KESISTING METAL.

Application filed November 10, 1924. Serial No. 748,941. I

Our present invention relates particularly to the protection against corrosion of iron and steel, but may be applicable to other metals as well.

Iron and steel are often used in places .where the metal is not only subject to ordinary atmospheric corrosion or rusting, but also to more active chemical action by fumes or corrosive liquids. Under the combined action of these deteriorating agencies, the life of articles made of ferrous metal is likely to be very short. Ordinary rustproofing treatment will effect but little improvement as the coating agents used for rust-proofing usually will not Withstand the corrosion caused by acid fumes or thelike.

In accordance with our invention we have provided a composite coating which will withstand both the conditions leading to rusting and also acidic corrosion. Thisv coating comprises a layer of a rust-proofing metal, such for example as cadmium, overlaid by a layer of a metal capable of withstanding acids, as tin, for example.

A practical utilization of' ur invention 1s illustrated by the accompanying drawing which shows in perspective a trolley wire hanger as an example of an object coated in accordance with our invention with the above attendant advantages.

In carrying out our invent-loathe metal article is cleaned by theusual well known method ,to produce a surface condition suitable for electroplatirig.- A film of cadmium maybe applied by any well known method. For example, a plating bath comprising a solution in water of a cadmium salt, a cyanide and an alkali may be used. We have used the following Solution with success with a current densityof about 8 to 10 am-- peres per square foot:

Cadmium hydrate, 4 ounces; sodium cyanide. 6 ounces; caustic soda, 1 ounce; Water, 1 gallon. 4

The thickness of the cadmium film, of course, may be varied with conditions. WVe

in thickness produced by plating at the above current 'density' for about thirty minutes at room temperature is sufficient A -tin film may be applied by any ap provedmethod. For example a solution of the following composition'may be need:

Tin chloride, 2 ounces; -sodium cyanide,

ounce; caustic soda, 8 ounces; cream of tartar, 1 ounce; water, 1 gallon.

With a currentzdensity of ten amperes per square foot a suitable coating may be deposited from the above bath in about fifteen minutes at room temperature.

The electrolytic potential of tin with respect to a ferrous metal is so considerablethat a ferrous metal article coated with tin alone would be attacked very rapidly in the presence of an electrolytelsuch as water containing an acid wherever-the tin coating was locally imperfect due to wear, or an accidental scratch orany other reason. The

presence of the cadmium however will protect the ferrous metal even when the -.tin coating is marred. On the other hand, cadmium alone will not withstand as well as tin the influence of acidic corrosion.

Some of the benefits of our invention may be obtained by using zinc as the rust-proof ing'metal in place of cadmium and thereupon applying tin over the zinc coating, and

holding leather during the process of treat-.

ment. particularly when making the so-called patent leather. v

What we-claim as new .and desire to secure by Letters Patent of the United States,

An article of manufacture comprising a body ofv ferrous metal. a film of cadmium thereon and a film of tin overlaying said cadmium film. g

In witness Wh81' e0f, we have hereunto set our hands this 7th day of November. 1924. CHARLES E. JONES. MARK A. ATUESTA.

we desire the appended claims, therefore, to 

